Tracer diffusion in single crystalline CoCrFeNi and CoCrFeMnNi high-entropy alloys: Kinetic hints towards a low-temperature phase instability of the solid-solution?

Tracer-diffusion of constituting elements in single-crystalline CoCrFeNi and CoCrFeMnNi is measured from 923 K to 1373 K. In CoCrFeMnNi, low-temperature deviations from otherwise linear Arrhenius-type dependencies are seen for all elements excluding Mn. The kinks are prominent at about 1100 K for Co and Ni and at 900 K for Cr and Fe indicating the existence of a low-temperature modification of the equiatomic solid-solution phase in CoCrFeMnNi. The temperature-dependent correlation factors of all elements are determined within the framework of the random alloy model providing insights into potential mechanisms of the kinetic anomaly. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.